1. Focus on 2 to 3 keywords per page
Any more than that and the keywords will lose their impact -- and search engines may penalize those pages for keyword stuffing (a spammy practice that wont get you very far).
2. Keywords placement
Keywords should be near the beginning of your titles. Search engines "read" from left to right, so to say, just like we do.
Also place your keywords at the beginning, middle and end of your page or post. This shows the search engines that you're not just stuffing all of your keywords in at the beginning.
3. Use bold, italics, or heading tags
Search engines will pick up on the emphasis and may give those words or phrases some extra priority. (Read more about using h tags and alt tags for SEO).
It can also create a secondary reading path to help people skim through your content.
4. Use synonyms
Its going to looks silly using the same keywords over and over " the copy just wont read smoothly. Become friends with your thesaurus. After all, not everyone is searching the same exact search phrase: one person's "garbage can" is another's "waste basket".
5. Write for your readers first
The content has to make sense, and it has to be congruent with what the person was searching for. If not, they wont stay and they certainly wont become your customer.